Manufacture of articles from liquid dispersions



June 19, 19 45. V E. E. HABIB AL MANUFACTURE OF ARTICLES FROM LIQUID DISPERSIONS Filed Nov. 16, 1943 Z W F "PP "9 layer of Compound coogu/anf EMILE E. HAB/B GORDON E GOTT Inventors A/forney iect and particularly to the Patented June 19, 1945 musacruas or serious moss mum msrsasrons Emile E. Hablb and Gordon B. Gott. Arlington.

Masa. asslgnors to Dewey and A]!!! Che-u Company, North Cambridge. Illa. a corporation of Massachusetts Application Novensber is. ms, set-u a 8 Claims. (CL 1H) This invention relates to the manufacture of hollow rubber objects having an opening which is smaller than the greatest diameter of the obmanufacture of meteorological, radiosonde and life-saving balloons.

Balloons which are designed to carry recording instruments aloft are quite large. The common size is about 36 inches diameter before ascension and the envelopes must be capable of expanding to 12 feet or more to attain the necessary elevation before bursting. Dipping on molds as large as 36 inches in diameter is not a feasible commercial practice and building up balloons by cementing segments together is very expensive.

Such balloons have in the past been made by casting a natural latex dispersion containing a gelling agent in hollow molds which are rotated about two axes in. a hot water bath, and then thinning the wall and simultaneously bringing the balloon to the proper large size and shape by inflating it. As applied to natural latex, this process is satisfactory although slow. However, when natural latex became unavailable and it was necessary to turn to synthetic materials, serious process difliculties were encountered. In the case cause it permits I iects on forms which are flat in shape and of smaller sine than the nnished object. l'lat forms, of course. occupy less space in the dipping bath, so that many can be dipped at one time.

Itwasfurtherdiscoveredthatthesamemethod canbe appliedtonat'urallatexprovidedcertain limitations as to the amount of combined sulphur in the rubber hydrocarbon at the time of dipping are observed. as the result of a lengthy study of the changes which take place in compounded latex in transit and storage, we have discovered that the amount of combined sulphur in the rubber has an important effect on the tear-resistance of the'gel deposit and consequently on the possibility of stripping the gel from the form. Where a natural rubber dispersion is employed in which the combined sulphur is uniformly distributed among the rubber particles. it has been found that the deposited gel can be stretched at least 100%, provided the combined sulphur does not exceed a critical amount in the neighborhood of 0.45%. In referring to percentages of combined sulphur herein, we refer to the percentage of sulof polymerized chlor0prene-1,3, these difllculties I were caused primarily by spontaneous syneresis during casting, resulting in lack of uniformity in the finished film, by the instability of the dispersion after a gelling agent had been added to it,

and by the extreme sensitivity of the dispersion, which required an accuracy of control of time and temperature difllcult to achieve in plant practice.

-The-war-time development of the inflatable life-saving raft created a need for a captive-balloon to carry a radio antenna, which could be kept aloft for days at a time, even under the intense heat and light conditions encountered at sea in southern latitudes. Balloons made from natural rubber latex lose hydrogen by diffusion too rapidly and deteriorate too rapidly in sunlight to be useful for this purpose. It was found to be possible to make a polymerized chloroprene-l,3 balloon which is sufficiently age-resistant i'or the purpose, but again the same difficulties in factory-scale manufacture were encountered.

The present invention is based on the discovery that the deposit of polymerized halogen butadiene-l.3 gel formed on a balloon mold by dipping is sufilciently tear-resistant before dryin to permit it to be removed from a balloon mold by stretching and yet is soft and plastic enough to permit sufficient plastic flow so that it may be permanently enlarged and thinned and rendered more nearly of spherical shape by inflating it.

The inflation step is particularly important hephur combined with the rubber hydrocarbon, based on the dry weight of the rubber hydrocarbon. It has also been found that when the dipping bath is composed of a mixture of rubber particles of differing combined sulphur content the mixture must contain a suflicient proportion of rubber particles having a combined sulphur content of less than 0.45% so that a coherent gel may be formed of suillcient strength to withstand stretching at least 100% to get it of! the form. In general, we believe this condition is satisfied if the mixture contains enough low sulphur content rubber to form a continuous phase in the deposit.

It is customary in the dipped-goods industry for manufacturers to purchase their dipping compounds from suppliers who add sulphur, accelerators and pigments to the latex. Thereafter, some weeks pass between the time the original mix is made and the time that the compound is used by the goods manufacturer. When 'our process was tried with such commercial latex compounds,

it failed. The gels were invariably too weak tov be removed from the molds. 0n the other hand, it operated perfectly on compounds mixed in the laboratory and which were used without delay.

We believe that we are the flrst to discover that the very tender gels formed by coagulant dipping are tear-resistant enough to be removed from the mold by stretching, even though the diameter of the mold is considerably greater than that of the neck. and yet are plastic enough so the production of spherical obthat theycan be permanently thinned and shaped by inflation.

In the accompanying drawing the several steps of our improved process as applied to the manufacture of balloons are illustrated, as far'as possible, diagrammatically.

Figure 1 illustrates the coating of the mold with coagulant;

Figure 2 dipping of the coagulant-coated mold in the dispersion;

Figure 8 allowing the coagulant to diifuse uniformly through the deposit:

Figure 4 stripping the deposited gel from the mold; Y

Figure 5 inflating the object to thin it and give it, its required size with uniform wall thickness;

Figure 8 illustrates the drying step; and

Figure 7 illustrates the final step of vulcanizing the object.

In practicing the invention, the dipping mold is flrst coated with a layer of an appropriate coagulant by dipping it into a bath of the coagulant, the coagulant allowed to dry somewhat, and the mold dipped in the dispersion long enough to build up a deposit of the required thickness. The mold is then withdrawn from the dispersion and the coagulant allowed to diffuse throughout the deposit, thus coagulating the liquid film of uncoagulated dispersion which remains on the surface of the gel when the mold is withdrawn from the latex. When the deposit is uniformly coagulated, it will be found to be sufllciently tearresistant to permit it to be stripped from the mold by stretching. After the object, for instance, a balloon, has been removed from the mold it is inflated to a predetermined extent while the gel is still sufficiently soft to permit plastic flow. It is then dried, which fixes it size, and later deflated and vulcanized. The plastic flow of the wall of the balloon during inflation permanently thins the wall so that the balloon assumes the desired larger size.

The invention will be further understood from the following examples which are given by way of illustration:

Example 1.For a meteorological balloon made from a polymerized chloroprene-l,3 latex compound.

A dipping compound is made up in accordance with the following formula:

Parts by weight of solids Polymerized chloroprene-1,3 dispersion (neoprene type 571) Dibutyl sebacate emulsion 15 NH; (as ammonium hydroxide) 0.2 Hard clay (Buprex brand) 7 Dispersing agent (formaldehyde condensation product of naphthalene sulfonic acid) 0.14 Zinc oxide (Kadox) 5.00 Phenyl beta naphthylamine 2.00 Casein solution (10 per cent) 0.35

129.77 The dibutyi sebacate emulsion has the following formula:

. Parts by weight Dlbutyl sebacate 35.00 Oleic acid 1.10 Wetting agent 0.10 nium hydroxide (28%) 1.10 Water 13.05

The team. for the casein solutionis as 101- lows: 1

' I Parts by'wclght Casein 3.50 Water 837.50 Ammonium hydroxide (28%) 7.50

, state The formula for the coagulant is as follows:

. Parts by weight Bentonite Water 900 Acetone 1321 Calcium nitrate tetra hydrate 1250 Glycerine 55 0 sets latex and the coagulant is allowed to diil'use through the deposited gel, as indicated in Figure 3, thus coagulating the layer of uncoagulated dispersion which is on the surface of the gel at the moment when the mold is withdrawn from the bath. Next, the neck is stretched to the maximum diameter of the mold, which is about flve times the size of the neck opening, and the balloon is pulled off or stripped from the mold as indicated in Figure 4. The presence of bentonlte in the coagulant coating makes the strip ping easier to perform. The gel is then inflated to the desired diameter as indicated in Figure 5,- while the deposited gel is still plastic. This inflation reduces the thicknessof the wall of the balloon while making it more nearly spherical in shape, and permanently increases its size. The balloon is then dried while still inflated, as indicated in Figure 5, and finally deflated and vulcanized by heating in dry air at a temperature of about 212 F., as indicated in Figure 7.

In the foregoing description, the process described is that which is employed in making balloons on forms the greatest diameter of which is 4 or 5 times that of the neck. The procedure is equally applicable to balloons having a relatively smaller maximum diameter and which consequently need not be stretched so severely.

Example Z.For a life-saving (captive) balloon to contain hydrogen:

Parts by weight of solids Polymerized chloroprene-1,3 dispersion (neoprene type 571) 100 Ammonia (as ammonium hydroxide)--- 0.28 Hard clay (Suprex brand) 7.00 Dispersing agent (formaldehyde condensation product of naphthalene sulfonic acid) 0.14 Zinc oxide (Kadox) 5.00 Phenyl beta naphthy1arnine 2.00 Casein solution 1 (10%) 0.35

The casein solution and coagulant have the composltion described in Example 1.

Procedure-The same as in vulcanization step is omitted.

trample 3.For a balloon made from natural rubber latex.

I be about 0.45%

Symmetrical di-beta-naphtbyl para phenvlene diamine 1.00

Formaldehyde condensation product of naphthalene sulfonlc acid 0.24 Titanium dioxide 1.00 sulphur 1.10

The amount will vary with dim-rout latices. Shillciont should be used to give the dispersion a viscosity suitable for dipping.

The coagulant has the following compositionzi The ingredients are added in the order stated. Procedure.--The dipping procedure is the same as in Example 1.

The sulphur in this dispersion will slowly comblue with the latex particles. When freshly prepared the compound contains substantially no combined sulphur. but the amount will be found to increase slowly until the bath finally becomes unusable, because gels deposited from it could not be stripped from the mold. The bath must be used. if it is to be used for making balloons in which the neck must be stretched as much as 100% to strip them from the molds, before the amount of combined sulphur reaches as much as 0.45%. Analysis of the above composition showed the amount of combined sulphur at the end of one day to be 0.18%. The compound was used at this time according to the procedure of Example 1. In stripping test objects from the mold, it was found that the objects could be stripped without tearing from forms having a greatest diameter five times the diameter of the neck. However, when the bath had aged for one day more, the combined sulphur was found to be 0.24%, and objects formed from the dispersion could not be stripped from 5 to 1 ratio forms but could be stripped from a 4 to 1 form. At the end of three days, the combined sulphur had increased to 0.38% and the specimens could be stripped from a form having a neck-greatest diameter ratio of 1 to 3 but not from one of 1 to 4 ratio. At the end of live days. the per cent of combined sulphur was 0.45% and the specimen could not be stripped from a mold having a stretching ratio of 1 to 3, but could Just be stripped from a mold'in which the ratio was only 1 to '2.- Atthe end of the sixth day the combined sulphur was 0.47 and the specimen could not be stripped from a mold having a ratio of neck opening to greatest diameter of 1 to 2.

These figures indicate how the tear-resistance of the deposited gel decreases as the compound ages and the tree sulphur combines with the rubber hydrocarbon until the rubber particles have ill lost their-coheslonto such an extent that the gel I stretched to any useful extent. Therefore. we conclude that in a uniform mixture the deposit ceases tohave the necessary tearresistance to permit strlppingwhen the combined sulphur exceeds a critical point which appears to and that the bath will be usable until the combined sulphur exceeds 0.45%.

While the herein-described process ispartlcularly applicable to 'polymerlaed halogen butadiam-1,3 and natural rubber. we believe it to be applicable to other elasiomers capable of being made into liquid dispersions from which tearresistant. coherent gels can be coagulated. Ac-

cordingly. in the"",foregoing specification and. claims. we have used word "rubber" in an inclusive sense.

While itis convenient to think of a; mold for .a balloon as spherlcalin shape with a.

neck, it is customaryihplant practice to use list or iluted molds. Accordingly, we have used the phrase "greatest diameter" to designate the greatest dimension o t-the mold which must pass through the neck opening. 1

When the stripped gel is to be enlarged from a small to a large area,erelnoval of the deposit from the mold while the net form of the gel is conserved by keeping the interstices'of the net filled or distended with an "intervenor," as it is called by Beckmann, U. S. Patent No. 1,745,657, is necessary. It is not essential that all of the water which originally formed the continuous phase of the dispersion should be conserved, but it is essential that a large proportion-at least enough to allow plastic movement of the rubber a gregates in the areas which are to be expanded-be conserved to permit uniform expansion of the gel. Herein, we refer to a gel. in this condition as a "plastic ge While excellentballoons may be made by the casting process from natural rubber. and probably satisfactorily from polymerized chloroprene- 1,3, casting is essentially a slow process since the objects are cast individually and the process does not lend itself readily to mass production. Our

improved process, on the other hand, is particularly adapted to mass production since the molds may be handled in gangs, as many as six hundred or more balloon molds being dipped at one time, and the stripping can be done with great rapidity. This great improvement in manufacture is made possible by our discovery that a. gel produced by dipping is sufllciently tear- -resistant to permit it to be stripped from the mold and yet is plastic enough to allow it to be subsequently enlarged and thinned by inflation.

7 We claim:

l. The process of making a hollow inflatable object having an opening which is less than one-,

half the greatest diameter of therobject which includes dipping a mold coated with coagulant and having a body of large diameter and a por- I tion shaped to form an opening less than onehalf the large diameter into a' liquid dispersion of rubber to form a deposit on the mold. withdrawing the mold ,irom the dispersion 'and stripping the depomted gel fromthe mold by stretching it while the deposit has enough water to allow plastic-flow in the areas which are to be expanded and prior to the deposit in the said areas which are to be expanded attaining any substantial elastic property.

2. The process of making a hollow inflatable object having an opening which is less than onehairthesreatestdiameteroitheobisctwhich includes dipping a mold coated with coagulant andhavingabodyoilargediameterandapob tion shaped to form an opening less than onehali'thelarsediameterintoaliquiddispersiono! rubber to form a deposit onthe mold. withdrawing the mold from the dispersion and stripping the deposited gel from the mold by. stretching it while the deposit has enough water to allow plastic flow in the areas which are to be expended and prior tothe deposit in the said areas which are to be expanded attaining any substantial elastic propert'mand inflating theobject while the deposited gel is still capable of plastic now.

3. The process of making a hollow inflatable object havingan opening which is lessthan oneform a deposit on the mold,

in; it while the deposit has'enough water to allow plastic flow in the areas which are to be expanded and prior to the deposit in the said areas which are to be expanded attaining any substantial elastic property, inflating the object while the deposited gel is still capable of plastic flow, and drying the inflated object and vulcanizing 4. Ihe process of making a hollow inflatable object hailing an opening which is less than onehalt the greatest diameter oi the object which includes dipping a mold coated with coagulant and having a body of large diameter and a portion shaped to form an opening less than onehalt the large diameter into a liquid dispersion of polymerized chloroprene 1.3 to form a deposit on the mold, withdrawing the mold iron the dispersion and stripping the deposited gel from the mold by stretching it while the deposit has enough water to allow plastic flow in the areas mold iron: the dispersion, stripping the gel from the mold by stretching it while posit has enough water to the areas which are to be expanded and prior to the deposit in the said areas which are to be expanded attaining any substantial elastic Property.

6. The process of making a hollow inflatable object having an opening which is less than onehalf the greatest diameter of the object, which includes preparing a liquid dispersion oi natural rubber containing sulphur, dipping a mold coated withcoaguiantandhavingabodyotlargediameter and a portion shaped to form an opening less than one-half the large diameter into said liquid dispersion oi natural rubber while the comper cent to form CERTIFI GATE GF CORRECTION.-

Patent No. 2,578,700,

EMILE E; HABIB ET AL.

It is hereby certified that error appears in the printed specification 'of the above numbered patent requiring correction as follows: Page 11., second column, line 37, beginning with the words in the" strike'out all to and including the syllable lowing "posit" in l,ine.l. .O, and insert instead the fol- --has enough water to' allow plastic flan in the areas which are to be expandedand 31-101- to the deposit in the said areas which are to be expanded-;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 2nd day of October, A. D.-19i4.5.

(Seal) Leslie Frazer First Assistant Commissioner of Patents.

hairthesreatestdiameteroitheobisctwhich includes dipping a mold coated with coagulant andhavingabodyoilargediameterandapob tion shaped to form an opening less than onehali'thelarsediameterintoaliquiddispersiono! rubber to form a deposit onthe mold. withdrawing the mold from the dispersion and stripping the deposited gel from the mold by. stretching it while the deposit has enough water to allow plastic flow in the areas which are to be expended and prior tothe deposit in the said areas which are to be expanded attaining any substantial elastic propert'mand inflating theobject while the deposited gel is still capable of plastic now.

3. The process of making a hollow inflatable object havingan opening which is lessthan oneform a deposit on the mold,

in; it while the deposit has'enough water to allow plastic flow in the areas which are to be expanded and prior to the deposit in the said areas which are to be expanded attaining any substantial elastic property, inflating the object while the deposited gel is still capable of plastic flow, and drying the inflated object and vulcanizing 4. Ihe process of making a hollow inflatable object hailing an opening which is less than onehalt the greatest diameter oi the object which includes dipping a mold coated with coagulant and having a body of large diameter and a portion shaped to form an opening less than onehalt the large diameter into a liquid dispersion of polymerized chloroprene 1.3 to form a deposit on the mold, withdrawing the mold iron the dispersion and stripping the deposited gel from the mold by stretching it while the deposit has enough water to allow plastic flow in the areas mold iron: the dispersion, stripping the gel from the mold by stretching it while posit has enough water to the areas which are to be expanded and prior to the deposit in the said areas which are to be expanded attaining any substantial elastic Property.

6. The process of making a hollow inflatable object having an opening which is less than onehalf the greatest diameter of the object, which includes preparing a liquid dispersion oi natural rubber containing sulphur, dipping a mold coated withcoaguiantandhavingabodyotlargediameter and a portion shaped to form an opening less than one-half the large diameter into said liquid dispersion oi natural rubber while the comper cent to form CERTIFI GATE GF CORRECTION.-

Patent No. 2,578,700,

EMILE E; HABIB ET AL.

It is hereby certified that error appears in the printed specification 'of the above numbered patent requiring correction as follows: Page 11., second column, line 37, beginning with the words in the" strike'out all to and including the syllable lowing "posit" in l,ine.l. .O, and insert instead the fol- --has enough water to' allow plastic flan in the areas which are to be expandedand 31-101- to the deposit in the said areas which are to be expanded-;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 2nd day of October, A. D.-19i4.5.

(Seal) Leslie Frazer First Assistant Commissioner of Patents. 

